/Engine/Plugins/FX/Niagara/Source/NiagaraEditor/Public/NiagaraNodeFunctionCall.h
Walk through the internal script graph for an ParameterMapGet nodes and see if any of them specify a default for VariableName.
[UEdGraphPin](API\Runtime\Engine\EdGraph\UEdGraphPin) * FindParameterMapDefaultValuePin ( const [FName](API\Runtime\Core\UObject\FName) VariableName, [ENiagaraScriptUsage](API\Plugins\Niagara\ENiagaraScriptUsage) InParentUsage, [FCompileConstantResolver](API\Plugins\NiagaraEditor\FCompileConstantResolver) ConstantResolver ) const